1. Field of the Invention
This invention relates to the processing of plastic materials.
2. Description of the Art Practices
It is known that polyvinylchloride may be prepared through an extrusion process to form useful articles such as combs, spoons, siding, window frames, moldings, pipes, tubing and many other useful items. The polyvinylchloride is prepared in the form of a shaped article by mixing the polyvinylchloride, applying sufficient heat and/or mechanical pressure to transform the granular or powdered form of the polyvinylchloride into a plastic state. The polyvinylchloride in the plastic state is then fed through an extruder which is basically described as a screw device which recieves the pulverant polyvinylchloride resin and such other necessary ingredients, and forces the resin through an orifice thereby forming the article.
It is known from the author's earlier U.S. Pat. No. 4,332,702, issued June 1, 1982 that partial esters of pentaerythritol may be used as a lubricant in processing polyvinylchloride. It is also known from U.S. Pat. No. 4,336,176, issued June 22, 1982 to the author that it is desirable to include organo-tin compounds and the aforementioned partial ester of pentaerythritol to obtain a stabilization effect in a polyvinylchloride shaped article.
It is currently known in the art that ethylene bis stearamid may be used as a lubricant, which when mixed with polyvinylchloride resin prior to extrusion will coat the extrusion device so that the polyvinylchloride does not adhere to the surfaces of the extruder. Ethylene bis stearamide has been found unsuitable in certain regards inasmuch as it is subject to degradation. The degradation is believed to occur at the amide linkage. During the degradation of ethylene bis stearamide it is theorized that the polyvinylchloride is damaged through the removal of chlorine molecule by the decomposing amide. The loss of the chlorine results in a rearrangement of the bond structure of the polyvinylchloride giving rise to unsaturation at the site where the chlorine atom was removed. The unsaturation leads to instability of the resin from sunlight.
Ethylene bis stearamide is believed to function in this mechanism as a reactant material; therefore the increased use of the amounts of the amide leads to further degradation of the polyvinylchloride. Unfortunately, for many applications ethylene bis stearamide is an unsuitable lubricant as the amount of that material which must be used is sufficient to damage the polyvinylchloride article in a short period of time. Polyethylene lubricants have been used in place of amide lubricant but are not as fully accepted as the amides.
Throughout the specification and claims, percentages and ratios are by weight and temperatures are in degrees Celsius. To the extent applicable, the foregoing references are herein incorporated by reference.